An aerogel is a superporous, high specific surface area material having a porosity of about 90 to 99.9% and a pore size in range of 1 to 100 nm, and is a material having excellent properties of ultra light weight, super insuation, ultra low dielectric constant and the like. Accordingly, research on the development of aerogel materials as well as research on the practical use thereof as transparent insulation materials, environmentally friendly high temperature insulation materials, ultra-low dielectric thin films for highly integrated devices, catalysts and catalyst carriers, electrodes for supercapacitors, and electrode materials for seawater desalination have been actively studied.
The biggest advantage of the aerogel is that the aerogel has a super-insulation exhibiting a thermal conductivity of 0.3 W/m·K or less, which is lower than that of an organic insulation material such as conventional Styrofoam, and that fire vulnerability and the occurrence of harmful gases in case of fire which are fatal weaknesses of the organic insulation material can be solved.
In general, the aerogel is produced by producing a hydrogel from a silica precursor such as water glass, alkoxysilane series (TEOS, TMOS, MTMS, etc.) and the like, and removing the liquid components in the hydrogels without destroying microstructures. Typical forms of the aerogel may be classified into three types: powder, granular, and monolith, and the aerogel is generally in the form of powder.
Particularly, tetra ethyl orthosilicate (TEOS) among silica precursors is a material widely used in the industrial fields which produce a coating agent, an insulation material, porous ceramic and the like. In the market, various products such as pure TEOS, condensed TEOS, pre-hydrolyzed TEOS (HTEOS) and the like are on sale.
Among them, HTEOS is an ethyl polysilicate oligomyer material having a broad molecular weight distribution. When HTEOS is synthesized in the form of oligomer from TEOS monomer, physical properties such as gelation time and the like may be controlled, so that HTEOS may be easily applied in accordance with the user's reaction condition. In addition, HTEOS has the advantage of making the reproducible properties of the final product.
The HTEOS is generally synthesized by condensation reaction of TEOS which has passed through a partial hydration step under acidic conditions. In this case, the condensation reaction proceeds in a reflux reaction under acidic conditions, so that there is a disadvantage that the condensation rate is very slow. On the other hand, a condensation catalyst may be used in order to increase the condensation rate. However, in this case, it is difficult to control the molecular weight of the reaction product, and the occurrence of the production cost of the catalyst and the addition of the catalyst separation process must be required in the synthesis step, so that there is a disadvantage in that the process is complicated and the manufacturing cost is increased.
Accordingly, the inventors of the present invention have developed a novel method for synthesizing a pre-hydrolyzed alkyl polysilicate in which through the addition of the silica precursor in two steps, the condensation reaction time is remarkably shortened compared with the conventional synthesis method, and the condensation catalyst is not used, so that the process is simple and the production cost can be remarkably reduced.